How is a TLOC uniquely identified from a WAN Edge router to the SD-WAN transport network?

The SD-WAN site ID identifies a logical site, not a specific TLOC on a router.

OMP (Overlay Management Protocol) is the routing protocol that advertises TLOCs and routes, but it is not one of the three components that uniquely identify a TLOC itself.

In Cisco SD-WAN, a TLOC (Transport Locator) is uniquely identified by a combination of the WAN Edge router's System IP address, a 'color' which identifies the transport network, and the 'encapsulation' type. The System IP address is a stable, loopback IP address that uniquely identifies the router within the overlay, forming a critical part of the TLOC identifier.

A VPN ID identifies a specific VPN segment within the overlay network, not the physical transport location (TLOC) of a router.